Karl Rahner, S.J., editor, The pastoral approach to atheism (Paulist: NY 1967)

No question is more important and topical for the Church today than the question of how to approach the problem of atheism spiritually and pastorally. Vatican Council II did indeed touch upon it, but only on the periphery of the dominant theme of the Council. ... in a way that underrates the decisive issue of atheism in its peculiar form and menace. All other questions yield to this one. 1

Karl Rahner, S.J., What does Vatican II teach about atheism?

Once we have established that according to the Council's teaching an atheist is not necessarily "lost" because of his atheism, even if he dies an atheist, the theological problem arises whether "goodwill" can be a simple substitute for knowledge of God and faith in God. We have already seen that n.7 of the Decree on the missionary activity of the Church maintains that all men can be saved, and we have included the atheist if there is no moral guilt. But the Decree says explicitly that persons, here referred to, can attain to salvation precisely because they achieve a saving faith, although in ways that are only known to God. Therefore the question is whether and how an atheist in general can be assumed to have such a faith. ...

The conciliar texts quoted above constantly mention such an atheist as acting according to his conscience, as seeking the truth, as fulfilling the requirements of his moral conscience. In this way he can indeed be thought of as innocent and within reach of divine intent of salvation because, although he has not (yet) found God, he follows the demands of his conscience. 14-5